The CITE Conformance Tests of the Open Geospatial Consortium are the best functional tests we have of GeoServer

The cite/ directory is especially useful for setting up the tests on PostGIS. The other DataStores will not work as well, not because we are not extremely confident in them, much more because CITE is extremely rigid about the data that must be used and implicitly imposes a number of requirements, for example the server must support more than 10 characters for attributes, which shapefiles do not support (at least not without implementing non open standard helper files). For open source tests, we highly recommend the WMS and WFS suites developed as part of the ACE-GIS project. They are available online. And if you are interested in the source files and running them yourselves, then email the list, as we have access to them, and indeed are looking to make them available for download on the GeoServer community site.

For 1.4.x, we do the WMS 1.1.1 and WFS 1.0 tests. For 1.5.x we should start doing the WCS tests, and we are helping to develop the WFS 1.1 tests as part of an OGC project - the code should be released after 1.5.

The tests are run by putting a GeoServer instance on a public IP address with the pre-configured data that we provide. For information on actually setting up and running the tests, go to Running CITE Tests.